Causes and Countermeasures of common faults of the

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Causes and Countermeasures of common faults in gravure printing (Part 1)

key words: plastic film, plastic printing fastness, overprint accuracy

I. back adhesion

after printing, the imprinted surface of plastic film or transparent paper has the illusion of dryness, but after printing the drum or bag, the back surface is sticky and dirty during storage. In case of serious problems, the printing pieces cannot be torn apart, and the ink layer of graphics and texts moves, resulting in product scrap. This phenomenon is more likely to occur in the high temperature season, but high temperature is not the only reason for the back adhesion. The back adhesion is also closely related to a series of factors such as plastic but a few enterprises' business difficulties, ink, solvent, air volume, light, speed and so on

(1) the solvent is not completely volatilized

① plastic film printing uses solvent evaporation to dry the ink. Its volatilization speed determines the drying of the ink layer. Its volatilization rate is an important factor that determines the drying condition of the ink layer and affects the printing quality. The slower the solvent volatilizes, the better the reproducibility of the plate, the more beautiful the printing color, but it is easy to adhere in the verification work; On the contrary, there will be imprinting and whitening. Therefore, the key to gravure printing of plastic film is to choose the solvent with appropriate evaporation rate. In continuous chromatic printing, the solvent must be completely volatilized during the running time between the two printing stations, otherwise, the roller will stick when printing at the next station

② after film printing, the organic solvent in the ink is not completely volatilized in the drying system, and there is still residual heat after the film is rolled, which brings conditions for the solvent remaining in the ink layer to continue volatilizing, thus forming adhesion

③ in high temperature and wet seasons, the film is rolled too tightly or pressed after printing

countermeasures: the evaporation rate of the solvent in the ink depends not only on the boiling point, vapor pressure and latent heat of the solvent once the material is crushed (if necessary). It also depends on the temperature, humidity, air volume, solute and ink layer thickness of the operating environment. Therefore, the evaporation rate of the solvent in the ink should be adjusted at any time according to the changes of conditions. At normal temperature, if the ink layer dries too fast, add a solvent with slow evaporation (such as Shanghai made 74-92 plastic film slow drying thinner), otherwise, add a solvent with fast evaporation (such as 74-91 plastic film fast drying thinner). It can also be diluted with mixed solvents of xylene, ethanol and isopropanol (the three solvents are mixed in the proportion of 1/3 each, and using a single solvent is not as good as a mixed solvent). If you feel that the drying is too fast, you can use a little butanol to replace some ethanol (butanol can increase the gloss of ink). But be sure to add the appropriate amount to avoid affecting the drying of the printing

the solvent used for gravure printing of plastic film is mainly alcohol with benzene. Alcohols are mostly ethanol and isopropanol, and benzene is mostly toluene and xylene. Due to the need of nitrocellulose, esters such as ethyl acetate and butyl acetate should also be added

comparison of volatilization rate of common solvents:

solvent name temperature (℃) volatilization rate (s) toluene 3031 xylene 3070 Quzhou Yuanli scrap purchase reduced by 20 yuan/ton; Guangxi Wuzhou Yongda scrap purchase price fell 10 yuan/ton isopropyl alcohol 3055 ethanol 3047 butanol 30147 ethyl acetate 3018 butyl acetate 3070 (to be continued)

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